There are plastic switchguards available which are like small boxes with
hinged lids which fasten to the coverplate screws. You can pop open the
cover with your fingers to get at the switch, but it takes some intention.
I've used them for kitchen disposal switches and similar applications.

Take a look at these:

http://www.sportys.com/acb/showdetl....&st=7916&st2=-
41768417&st3=67972723&Product_ID=53&CATID=1&test=t estpl

Or this (same item at higher price, but shorter URL):
http://www.babyguard.com/swlogu.html